In UV curable cationic coatings, photoinitiators generate cationic species, which then function as catalysts for cationic polymerization. Epoxides, in particular cycloaliphatic epoxides, are the major reactive monomer/oligomers used for cationic UV cured coatings.
Typically, two types of crosslinkers are available for these coatings, low molecular weight alcohols and high molecular weight polyols. High molecular weight polyol crosslinkers, such as polyester, polyether, or caprolactone polyols, provide excellent flexibility; however, they are generally viscous, and as a consequence increase application related problems. Low molecular weight alcohols can reduce the viscosity of the coating formulations. However, they are volatile and lack the flexibility needed for most coating applications.
Homo- or copolyethers of 1,3-propanediol also can be used as crosslinkers for cationic UV curable coatings. However, they would have a greater effect if their functionality could be increased from the original 2 (i.e., 2 hydroxyls per molecule). Moreover, conversion of the hydroxyl end groups to a non-hydrogen bonding species would also serve to reduce viscosity.
U.S. Pat. No. 3,833,512 discloses organosilicon polymers containing monomeric units (A), (B) and (C) where (A) is an inorganic tetravalent silicon containing units, where all valencies of the Si atoms are saturated by oxygen linkages, (B) is polyvalent silicon containing units where 2-3 valencies of the silicon are linked to oxygen and at least 1 is linked to a carbon atom of an organic group containing a poly(oxyalkylene) chain, and (C) is monovalent silicon containing units where 1 valency is linked to oxygen and the other 3 are saturated by monovalent organic compounds, the mole ratio (A) to (B) to (C) being 0.4-2:1:0.2-2 respectively.
U.S. Pat. No. 6,737,482 discusses curable resin compositions comprising: (1) a reactive silicon group containing polyoxyalkylene polymer and epoxy resin, wherein the introduction rate of the reactive silicon into a molecular chain terminus is not less than 85% as analyzed by NMR spectroscopy, and (2) an epoxy resin.